bug#47895: 28.0.50; Emacs should only animate images that are visible

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: 47895@debbugs.gnu.org
> Date: Mon, 19 Apr 2021 22:49:55 +0200
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > I'd be interested to see a backtrace for such animation of an image
> > that is not on display.  In general, since animation is triggered (I
> > think) when the image is being prepared for redisplay, what you
> > describe shouldn't be happening.  If it dies indeed happen, I have a
> > couple of guesses how that could be triggered, but it would be nice to
> > see evidence.
> 
> I unfortunately don't have the time to debug right now, but it's easy
> enough to reproduce:
> 
> (progn
>   (eww "https://lars.ingebrigtsen.no/wp-content/uploads/2018/03/candid.gif";)
>   (bury-buffer))
> 
> This will leave you with an Emacs that uses at least 99% CPU, even if
> the eww buffer isn't even displayed.  (At least on this Debian/bullseye
> system, starting from -Q.)

Thanks, I will take a look when I have time.